Developers have tried for years to deliver applications with desktop-like features and quality through a web browser. In the early days HTML was simply not up to the task. The original solution was to use Java to run an app inside the browser but that, unsurprisingly, resulted in a horrible user experience. Later Flash appeared. Flash provided a much higher quality experience because the Flash browser plugin could do just about anything in terms of the user interface while still providing the benefit of deploying the app through a browser. Java and Flash are similar in concept but one was developed by a company that primarily made servers while the other was developed by a company that exclusively made desktop software. It's not a shock that Flash has a better user experience.
But Flash is not without downsides. First, the user has to have the Flash plugin installed. Second, the plugin has to load some or all of the application from the server to the user's browser. This often results in the user waiting through an annoying loading progress thermometer. Flash also crashes too often. Over the years, some people have told me that they don't install Flash because their entire system becomes unstable if they do. In addition, Flash and similar technologies like Microsoft's Silverlight are not efficient on mobile devices which are sensitive to battery life. Apple famously chose to not support Flash on iOS because it was felt that Flash was just not efficient enough.
Here at Real Software, long before there was an iPhone, we considered giving Real Studio users the ability to build applications that could be deployed in a browser via a special plugin we would develop. After much consideration, we decided not to pursue this for many reasons- one of which being we believe that depending on an installed plugin greatly reduces the value of the technology.
Now Adobe has announced that it's discontinuing the Flash plugin for mobile devices. It also appears that Microsoft may be putting Silverlight out to pasture as well. Adobe is going to refocus on HTML5. If Microsoft is going to end development of Sliverlight, perhaps they plan to do the same. This will likely be the beginning of the end for Flash as a plugin for desktop browsers as well. If Flash is going to support HTML5 for mobile, where all relevant browsers support HTML5, it's only a matter of time before the majority of desktop users are using an HTML5-compatible browser. At that point, it would not make sense for Adobe to continue to support a Flash browser plugin at all.
What we are seeing today with this announcement from Adobe and the rumors about Silverlight is technological equivalent of survival of the fittest and this time the winner is HTML5.